Electro-optical device, image printing apparatus, and method of manufacturing electro-optical device

ABSTRACT

An electro-optical device includes an electro-optical panel which has a plurality of electro-optical elements whose light-emitting characteristics or transmissive characteristics are changed by electrical energy applied; a converging lens array which has a plurality of distributed index lenses, each transmitting light traveling in the electro-optical panel to form an erect image with respect to an image on the electro-optical panel, the images formed by the plurality of distributed index lenses constituting a continuous image; and a transmissive spacer unit which is provided between the electro-optical panel and the converging lens array so as to be bonded to them. The spacer unit includes a laminated structure of a plurality of transmissive spacer members.

BACKGROUND

1. Technical Field

The present invention relates to an electro-optical device provided withan electro-optical panel having electro-optical elements, such aslight-emitting elements or light valve elements, therein, to an imageprinting apparatus using an electro-optical device, and to a method ofmanufacturing an electro-optical device.

2. Related Art

There has been developed a technique for using an electro-luminescentelement (hereinafter, referred to as ‘EL elements’) array to write anelectrostatic latent image on an image carrier (for example, aphotosensitive drum) of an image printing apparatus using anelectrophotography method. In this technique, generally, a converginglens array is provided between the EL element array and the imagecarrier (for example, see JP-A-63-103288 and JP-A-2004-58448 (FIG. 7)).For example, SLA (SELFOC lens array) available from Nippon Sheet GlassCo., Ltd. is used as an example of the conversing lens array (SELFOC isa registered trade mark of Nippon Sheet Glass Co., Ltd.).

FIG. 1 is a perspective view schematically illustrating a portion of animage printing apparatus using the converging lens array according tothe related art. In the image printing apparatus, a converging lensarray 40 is provided between a photosensitive drum 110 and alight-emitting panel 12 provided with the EL element array. Lightemitted from the EL element array of the light-emitting panel 12 passesthrough a plurality of distributed index lenses of the converging lensarray 40 to reach the photosensitive drum 110.

In general, the image printing apparatus is designed such that the idealvalue, that is, the design value of an object distance L_(o) of theconverging lens array to an object is equal to the ideal value, that is,the design value of an object distance L₁ to an image. Therefore, whenthe converging lens array 40 is provided between the light-emittingpanel 12 and the photosensitive drum 110, a distance between an incidentpoint of light on the converging lens array 40 and the EL element arrayis generally equal to a distance between an emission point of light fromthe converging lens array 40 and the photoreceptor 110, serving as animage carrier.

However, since an air layer having the same thickness as the objectdistance L_(o) exists between the incident point of light on theconverging lens array 40 and the EL element array, some of lightcomponents emitted from the EL elements are not incident on theconverging lens array 40. That is, this structure has a problem in thatthe usage efficiency of light is deteriorated.

SUMMARY

An advantage of some aspects of the invention is that it provides anelectro-optical device capable of reducing the loss of light, an imageprinting apparatus using an electro-optical device, and a method ofmanufacturing an electro-optical device.

According to an aspect of the invention, an electro-optical deviceincludes an electro-optical panel which has a plurality ofelectro-optical elements whose light-emitting characteristics ortransmissive characteristics are changed by electrical energy applied; aconverging lens array which has a plurality of distributed index lenses,each transmitting light traveling in the electro-optical panel to forman erect image with respect to an image on the electro-optical panel,the images formed by the plurality of distributed index lensesconstituting a continuous image; and a transmissive spacer unit which isprovided between the electro-optical panel and the converging lens arrayso as to be bonded to them. The spacer unit includes a laminatedstructure of a plurality of transmissive spacer members.

Here, the term ‘electro-optical elements’ means elements whose opticalcharacteristics (emission characteristics or transmissivecharacteristics of light) are changed according to electrical energyapplied. The elements whose optical characteristics are changedaccording to electrical energy include light-emitting elements (forexample, electro-luminescent elements and plasma display elements) forconverting electrical energy into optical energy and light valveelements (for example, pixels of a liquid crystal display device andpixels of an electrophoresis display device) whose transmittances arechanged according to electrical energy. The term ‘electro-optical panel’means a panel having an electro-optical device array provided therein.The term ‘bonding’ includes a state in which the spacer unit is directlybonded to the electro-optical panel and the converging lens array and astate in which the spacer member is bonded to at least one of theelectro-optical panel and the converging lens array with a transparentadhesive interposed therebetween.

According to the above-mentioned structure, the spacer unit having aplurality of spacer members is provided between the electro-opticalpanel and the converging lens array, which makes it possible to improvethe ratio of light incident on the converging lens array to lightemitted from the light-emitting panel (or light passing through theelectro-optical panel) and thus to raise the usage efficiency of light.When a transparent spacer unit (which may include a transparentadhesive) is interposed between the electro-optical panel and theconverging lens array, a gap between the light-emitting panel and theconverging lens array suitable for focusing an image of thelight-emitting panel on the converging lens array increases, comparedwith the case in which only the air layer is provided therebetween. Fromanother viewpoint, when the gap between the light-emitting panel and theconverging lens array is fixed and the gap is larger than the actualobject distance of the converging lens array to the light-emitting panelin the air, a spacer unit which is formed by laminating spacer membersand has a proper thickness (which includes a transparent adhesive) isprovided between the light-emitting panel and the converging lens arrayto increase the actual object distance. This structure enables theactual object distance to be equal a fixed gap between thelight-emitting panel and the converging lens array.

In the above-mentioned structure, it is preferable that the spacer unithave a light absorbing layer formed on a surface thereof not facing theelectro-optical panel and the converging lens array. According to thisstructure, it is possible to prevent light from being incident on theconverging lens array due to the internal reflection from the surface ofthe spacer unit not facing the electro-optical panel and the converginglens array. Therefore, it is possible to prevent an image formed by thereflected light from being mixed with an image formed by the lightemitted from the electro-optical panel to the converging lens arraythrough the spacer unit.

Further, in the above-mentioned structure, it is preferable that thespacer unit be provided with a receiving hole into which a transparentadhesive for adhering at least one of the electro-optical panel and theconverging lens array to the spacer member is filled. According to thisstructure, since the adhesive is hardened in the receiving hole, it ispossible to improve the appearance of an electro-optical device.

Furthermore, in the above-mentioned structure, it is preferable that atleast one of the electro-optical panel and the converging lens array befitted into the receiving hole. According to this structure, it ispossible to accurately arrange at least one of the electro-optical paneland the converging lens array on the spacer unit.

Moreover, in the above-mentioned structure, it is preferable thatconcave portions into which the adhesive flows from the bottom of thereceiving hole be formed in a side surface of the receiving hole of thespacer unit. It is difficult to arrange the adhesive before hardened inonly necessary portions of the receiving hole since the adhesive hasfluidity. However, the residual adhesive is filled into the concaveportions formed in the side surface of the receiving hole. In this way,it is possible to reduce the amount of the adhesive flowing outside thereceiving hole to the minimum and thus to improve the appearance of anelectro-optical device.

Further, in the above-mentioned structure, it is preferable that groovesinto which a transparent adhesive for adhering at least one of theelectro-optical panel and the converging lens array to the spacer unitflows be formed in a surface of the spacer unit facing at least one ofthe electro-optical panel and the converging lens array. It is difficultto arrange the adhesive before hardened in only necessary portions ofthe spacer unit since the adhesive has fluidity. However, the residualadhesive is filled into the grooves formed in spacer unit. In this way,it is possible to reduce the amount of the adhesive flowing from the gapbetween the spacer unit and the electro-optical panel or the converginglens array to the outside to the minimum and thus to improve theappearance of an electro-optical device. In the electro-optical deviceaccording to this aspect, it is preferable that, when the refractiveindex of each transmissive element provided between electro-opticalelements of the electro-optical panel and the converging lens array isn_(i), the thickness of each transmissive element is d_(i), the numberof transmissive elements is m, and an object distance of the converginglens array to the electro-optical panel in the air is Lo, the expression1 be satisfied. $\begin{matrix}\lbrack {{Expression}\quad 1} \rbrack & \quad \\{{0.9 \times {\sum\limits_{i = 1}^{m}\frac{d_{i}}{n_{i}}}} \leq L_{o} \leq {1.1 \times {\sum\limits_{i = 1}^{m}\frac{d_{i}}{n_{i}}}}} & (1)\end{matrix}$

When the expression 1 is satisfied, an image on the electro-opticalpanel can be substantially focused on the converging lens array. Theobject distance L_(o) used in the expression 1 may be the design valueof the object distance L_(o) or may be a value obtained by actualmeasurement.

Further, according to another aspect of the invention, an image printingapparatus includes image carriers; charging devices that charge theimage carriers; the electro-optical device according to claim 1 thatradiates light emitted from the electro-optical panel to the converginglens array onto charged surfaces of the image carriers to form latentimages thereon; developing devices that attach a toner on the latentimages to form toner images on the image carriers; and a transfer devicethat transfers the toner images from the image carriers to anotherobject. According to the image printing apparatus of this aspect, it ispossible to improve the usage efficiency of light.

Furthermore, according to still another aspect of the invention, thereis provided a method of manufacturing the electro-optical deviceaccording to claim 1. The manufacturing method includes laminating aplurality of spacer members such that the spacer members are bonded toeach other; bonding any one of the spacer members to the electro-opticalpanel; and bonding another member of the spacer members to theconverging lens array. Here, the laminating the spacer members such thatthe spacer members are bonded to each other, the bonding any one of thespacer members to the electro-optical panel, and the bonding anothermember of the spacer members to the converging lens array may beperformed randomly or at the same time. The method of manufacturing theelectro-optical device according to the invention makes it possible toimprove the usage efficiency of light.

Moreover, according to this aspect, it is preferable that the method ofmanufacturing the electro-optical device further include measuring anactual object distance L_(o) of the converging lens array to theelectro-optical panel in the air; and calculating the thickness of thespacer unit to be used, on the basis of the object distance L_(o) andthe refractive indexes of the spacer members, so as to satisfy theexpression 1.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a perspective view schematically illustrating a portion of animage printing apparatus according to the related art.

FIG. 2 is a perspective view schematically illustrating anelectro-optical device according to an embodiment of the invention.

FIG. 3 is a perspective view schematically illustrating a converginglens array used for the electro-optical device according to theembodiment of the invention.

FIG. 4 is a plan view of the electro-optical device shown in FIG. 2.

FIG. 5 is a cross-sectional view taken along the line V-V of FIG. 4.

FIG. 6 is a front view of the electro-optical device shown in FIG. 2.

FIG. 7 is a cross-sectional view illustrating spacer members used forthe electro-optical device shown in FIG. 6.

FIG. 8 is a diagram schematically illustrating an example of the path oflight when a solid transmissive element and an air layer are providedbetween the actual emission position and a distributed index lens of theconverging lens array such that the transmissive element is adjacent tothe emission position.

FIG. 9 is a diagram schematically illustrating an example of the path oflight when the solid transmissive element and the air layer are providedbetween the actual emission position and the distributed index lens ofthe converging lens array such that the transmissive element is adjacentto the distributed index lens.

FIG. 10 is a diagram schematically illustrating an example of the pathof light when the solid transmissive element and the air layer areprovided between the actual emission position and the distributed indexlens of the converging lens array such that the transmissive element isseparated from the emission position and the distributed index lens.

FIG. 11A is a diagram schematically illustrating an example of the pathof light when two transmissive elements having the same refractive indexare provided between the actual emission position and the distributedindex lens of the converging lens array.

FIG. 11B is a diagram schematically illustrating an example of the pathof light when two transmissive elements having different refractiveindexes are provided between the actual emission position and thedistributed index lens of the converging lens array.

FIG. 12A is a diagram illustrating outmost light components which areemitted from one spot to the distributed index lens to be focused on aphotosensitive drum when only an air layer is provided between theconverging lens array and a sealing member of the light-emitting panel.

FIG. 12B is a diagram illustrating outmost light components which areemitted from one spot to the distributed index lens to be focused on aphotosensitive drum when a spacer member is provided between theconverging lens array and a sealing member of the light-emitting panel.

FIG. 13 is a side view illustrating spacer members constituting a spacerunit which is interposed between the light-emitting panel and theconverging lens array.

FIG. 14 is a side view illustrating the spacer unit formed by bondingthe spacer members.

FIG. 15 is a side view illustrating the spacer unit to which theconverging lens array is bonded.

FIG. 16 is a side view illustrating an electro-optical device obtainedby bonding the converging lens array and the light-emitting panel to thespacer unit.

FIG. 17 is a front view illustrating the electro-optical device shown inFIG. 16.

FIG. 18 is a side sectional view illustrating a state in which theconverging lens array is adhered to the spacer unit having a receivinghole for receiving an adhesive.

FIG. 19 is a plan view of FIG. 18.

FIG. 20 is a front sectional view of FIG. 18.

FIG. 21 is a plan view illustrating a modification of the receiving holefor receiving an adhesive.

FIG. 22 is a front sectional view illustrating the modification of thereceiving hole for receiving an adhesive.

FIG. 23 is a side sectional view illustrating a state in which theconverging lens array is adhered to another spacer unit having areceiving hole for receiving an adhesive.

FIG. 24 is a front sectional view of FIG. 23.

FIG. 25 is a side sectional view illustrating a state in which theconverging lens array is adhered to still another spacer unit having areceiving hole for receiving an adhesive.

FIG. 26 is a front sectional view of FIG. 25.

FIG. 27 is a plan view illustrating a spacer member having grooves forcontaining an adhesive in both surfaces thereof.

FIG. 28 is a cross-sectional view of FIG. 27.

FIG. 29 is a plan view illustrating the adhesive arranged on the spacermember shown in FIG. 27.

FIG. 30 is a plan view illustrating the converging lens array arrangedon the spacer member shown in FIG. 27.

FIG. 31 is a front sectional view illustrating an electro-optical devicehaving the spacer member shown in FIG. 27.

FIG. 32 is a longitudinal sectional view illustrating an example of animage printing apparatus using the electro-optical device according toany one of the first to fifth embodiments of the invention.

FIG. 33 is a longitudinal sectional view illustrating another example ofthe image printing apparatus using the electro-optical device accordingto any one of the first to fifth embodiments of the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Structure of Electro-Optical Device

FIG. 2 is a perspective view schematically illustrating anelectro-optical device 10B according to an embodiment of the invention.The electro-optical device 10B shown in FIG. 2 is used as a linearoptical head for writing a latent image on an image carrier (forexample, a photosensitive drum 110 shown in FIG. 2) in an image printingapparatus using an electrophotography method. The electro-optical device10B includes a light-emitting panel (an electro-optical panel) 12 havinga plurality of organic EL elements (electro-optical elements) arrangedon the same surface and a conversing lens array 40 overlapping thelight-emitting panel 12. A transmissive spacer unit 52 formed of, forexample, glass or plastic is interposed between the light-emitting panel12 and the converging lens array 40, and the spacer unit 52 has aplurality of laminated transmissive spacer members 56 and 58. Theconverging lens array 40 is arranged between the light-emitting panel 12having an EL element array provided therein and the photosensitive drum110. Light emitted from the organic EL element array of thelight-emitting panel 12 reaches the photosensitive drum 110 via thespacer unit 52 and a plurality of distributed index lenses of theconverging lens array 40.

As shown in FIG. 3, the converging lens array 40 includes a plurality ofdistributed index lenses 42. Each distributed index lens 42 is a gradedindex fiber which is formed such that a low refractive index is obtainedon the central axis, that is, on the optical axis and such that therefractive index increases as it becomes more distant from the centralaxis. The distributed index lens 42 transmits the light emitted from thelight-emitting panel 12 to form an erect image with respect to the imageon the light-emitting panel 12 on the photosensitive drum 110. Imagesobtained by the plurality of distributed index lenses 42 constitute acontinuous image on the photosensitive drum 110. For example, SLA(SELFOC lens array) available from Nippon Sheet Glass Co., Ltd. is usedas an example of the conversing lens array 40.

FIG. 4 is a plan view illustrating the electro-optical device. As shownin FIG. 4, the distributed index lenses 42 are arranged in two rows andin a zigzag pattern, and are fixed to a case of the converging lensarray 40 represented by a virtual line. Each distributed index lens 42overlaps a region in which an EL element 14 of the light-emitting panel12 is formed. The arrangement pattern of the distributed index lenses 42is not limited to the shape shown in FIG. 4, but the distributed indexlenses 42 may be arranged in other patterns, such as in one row or threeor more rows.

FIG. 5 is a cross-sectional view taken along the line V-V of FIG. 4. Asshown in FIG. 5, the light-emitting panel 12 includes a flat substrate18. The substrate 18 is formed of, for example, glass, plastic, ceramic,or metal. In addition, the substrate 18 may be formed of a transparentor opaque material. A driving element layer 20 is formed on thesubstrate 18, and a plurality of EL elements 14, serving aslight-emitting elements, are formed thereon. Each EL element 14 emitslight according to a voltage applied.

Although the inside of the driving element layer 20 is not shown indetail, the driving element layer 20 is provided with a plurality of TFT(thin film transistor) elements and wiring lines for supplying a currentto the TFT elements. The TFT elements supply a driving voltage to theindividual EL elements 14.

In this embodiment shown in the drawings, light emitted from the ELelements 14 travels in a direction opposite to the substrate 18, thatis, in the upper direction of FIG. 5. That is, the light-emitting panel12 is a top-emission-type OLED light emitting panel. Each EL element 14includes an anode 22 formed on the driving element layer 20, a holeinjecting layer 24 formed on the anode 22, a light-emitting layer 26formed on the hole injecting layer 24, and a cathode 28 formed on thelight-emitting layer 26. The cathode 28 is common to the plurality of ELelements 14.

In order to make the light emitted from the light-emitting layer 26travel in the upper direction, the anode 22 is formed of, for example, aconductive material having a reflective property, such as aluminum, andthe cathode 28 is formed of a transparent material, such as ITO (indiumtin oxide). The hole injecting layer 24 and the light-emitting layer 26are formed in a concave portioned defined by a partition wall 32 and aninsulating layer 30. The insulating layer 30 is formed of, for example,SiO₂, and the partition wall 32 is formed of, for example, polyimide.

The structure of each EL element 14 is not limited to theabove-mentioned structure. For example, the EL element 14 may have astructure in which an electron injecting layer is provided between thecathode and the light-emitting layer or a structure in which aninsulating layer is provided at a proper position.

Further, a sealing member 16 is bonded to the substrate 18. The sealingmember 16 protects the EL elements 14 from water and air, particularly,in cooperation with the substrate 18, to prevent them from beingdeteriorated. The sealing member 16 is formed of, for example, glass ortransparent plastic. The sealing member 16 is attached to the substrate18 by using an adhesive 34. For example, a thermosetting adhesive or anultraviolet-curable adhesive is used as the adhesive 34. As shown inFIG. 5, the adhesive 34 covers a portion of the driving element layer 20protruding from the sealing member 16.

In this embodiment, gap sealing is used. More specifically, an edgeportion of the sealing member 16 is bonded to the substrate 18 by theadhesive 34, and a space partitioned by the sealing member 16 and thesubstrate 18 is provided around the EL element 14. Preferably, a dryingagent is arranged in the space. In order to further protect the ELelements 14 from air, one or more passivation layers may be providedaround the sealing member 16.

The spacer member 54 of the spacer unit 52 is bonded to the sealingmember 16 of the light-emitting panel 12 by an adhesive 38. For example,a thermosetting adhesive or an ultraviolet-curable adhesive is used asthe adhesive 38. The sealing member 16 and the spacer member 54 of thespacer unit 52 may be directly bonded to each other without the adhesive38 interposed therebetween or may be bonded to each other with theadhesive 38 interposed therebetween. When the adhesive 38 is interposedbetween the sealing member 16 and the spacer member 54, a transparentadhesive 38 is used.

The spacer member 56 is bonded to the spacer member 54 by an adhesive38A. The spacer members 54 and 56 may be directly bonded to each otherwithout the adhesive 38A interposed therebetween or may be bonded toeach other with the adhesive 38A interposed therebetween. When theadhesive 38A is interposed between the spacer members 54 and 56, theadhesive 38A may be the same as the adhesive 38. The spacer member 54has a flat surface facing the sealing member 16 and the other flatsurface facing the spacer member 56. The spacer member 56 has a flatsurface facing the spacer member 54 and the other flat surface facingthe converging lens array 40.

The converging lens array 40 is bonded to the spacer member 56 of thespacer unit 52 by an adhesive 38B. The spacer member 56 of the spacerunit 52 and the distributed index lenses 42 of the converging lens array40 may be directly bonded to each other without the adhesive 38Binterposed therebetween or may be bonded to each other with the adhesive38B interposed therebetween. When the adhesive 38B is interposed betweenthe spacer member 56 and the distributed index lenses 42, the adhesive38B may be the same as the adhesive 38. In this embodiment shown in FIG.5, the spacer unit 52 has the two spacer members 54 and 56, but mayinclude three or more spacer members.

As the adhesives 38, 38A, and 38B, the following adhesives can be used:Optodyne UV-3200 (a registered trade mark) available from DaikinIndustries, Co., LTD., which is an ultraviolet-curable epoxy adhesivehaving a refractive index of 1.514 close to the refractive index ofglass after hardened; Optokleb HV153 (a registered trade mark) availablefrom Ardel, Co., LTD., which is an ultraviolet-curable epoxy adhesivehaving a refractive index of 1.63 higher than the refractive index ofglass after hardened; and Optodyne UV-4000 (a registered trade mark)available from Daikin Industries, Co., LTD., which is anultraviolet-curable epoxy adhesive having a refractive index of 1.567after hardened. However, the invention is not limited to theseadhesives.

In this way, light emitted from the EL elements 14 of the light-emittingpanel 12 is incident on the distributed index lens 42 through the spacerunit 52 overlapping the EL elements 14, as represented by arrow B inFIG. 5. Then, as shown in FIG. 6, the light passes through theconverging lens array 40 to reach the photosensitive drum 110.

As represented by a virtual line in FIG. 6, the light-emitting panel 12is attached to a cover 13, and the cover 13 covers all side surfaces ofthe light-emitting panel 12 and the converging lens array 40. The cover13 prevents external light from being incident on the converging lensarray 40 through, for example, the light-emitting panel 12 and thesealing member 16, thereby preventing the distortion of an image.Although the cover 13 is not shown in the other drawings, practically,the cover 13 is provided.

It is preferable that the electro-optical device 10B and the imageprinting apparatus according to this embodiment be designed so as tosatisfy the following expression 1. In the expression 1, ‘Lo’ indicatesan actual object distance of the converging lens array 40 to an object(to the light-emitting panel 12) in the air (see FIG. 1). In addition,‘n_(i)’ indicates a refractive index of each transmissive elementarranged between the EL elements 14 (particularly, the light-emittinglayer 26) of the light-emitting panel 12 and the converging lens array,and ‘d_(i)’ indicates the thickness of each transmissive elementarranged between the EL elements 14 (particularly, the light-emittinglayer 26) of the light-emitting panel 12 and the converging lens array.A subscript ‘i’ is an identifier for discriminating these transmissiveelements, and a character ‘m’ is the number of transmissive elements.

The image printing apparatus is designed such that the ideal value, thatis, the design value of the object distance of the converging lens array40 to an object is equal to the ideal value, that is, the design valuethereof to an image. The design value may be used as the object distanceL_(o) in the expression 1. However, the design values may be differentfrom each other due to a misalignment in manufacture. Therefore, it ispreferable to actually measure the object distance L_(o) of theconverging lens array 40 to an object (to the light-emitting panel 12)and to substitute it into the expression 1. When the expression 1 issatisfied, an image on the electro-optical panel is substantiallyfocused on the converging lens array 40. Further, when the distancebetween the converging lens array 40 and the photosensitive drum 110 isequal to the actual object distance of the converging lens array 40 tothe object (to the photosensitive drum 110) in the air, an imagecorresponding to the image on the electro-optical panel is formed on animage formation surface (in this embodiment, the photosensitive drum110) in a substantially focused state.

More preferably, the image printing apparatus is designed so as tosatisfy the following expression 2. When the expression 2 is satisfied,an image on the electro-optical panel is completely focused on theconverging lens array 40. The expression 1 is obtained by giving anallowable range of ±10% to the right side of the expression 2. How toobtain the expression 2 will be described later. $\begin{matrix}\lbrack {{Expression}\quad 2} \rbrack & \quad \\{L_{o} = {\sum\limits_{i = 1}^{m}\frac{d_{i}}{n_{i}}}} & (2)\end{matrix}$

Next, preferred design values of this embodiment will be described indetail with reference to FIGS. 2, 5, and 6. When the expressions 1 and2, which are general expressions, are applied to this embodiment, thefollowing expressions 3 and 4 are obtained:0.9×(d ₁ /n ₁ +d ₂ /n ₂ +d ₃ /n ₃ +d ₄ /n ₄ +d ₅ /n ₅ +d ₆ /n ₆ +d ₇ /n₇ +d ₈ /n ₈)≦L_(o)≦1.1×(d ₁ /n ₁ +d ₂ /n ₂ +d ₃ /n ₃ +d ₄ /n ₄ +d ₅ /n ₅+d ₆ /n ₆ +d ₇ /n ₇ +d ₈ /n ₈)  (3), andL _(o) =d ₁ /n ₁ +d ₂ /n ₂ +d ₃ /n ₃ +d ₄ /n ₄ +d ₅ /n ₅ +d ₆ /n ₆ +d ₇/n ₇ +d ₈ /n ₈  (4).

In these expressions 3 and 4, d₁ is the thickness of the cathode 28overlapping the light-emitting layer 26, and n₁ is the refractive indexof the cathode 28. d₂ is the thickness of an air layer arranged on theupper side of the light-emitting layer 26, and n₂ is the refractiveindex of the air layer (about 1). d₃ is the thickness of a portion ofthe sealing member 16 arranged on the upper side of the light-emittinglayer 26, and n₃ is the refractive index of the sealing member 16. d₄ isthe thickness of the transparent adhesive 38 between the sealing member16 and the spacer member 54. When the adhesive 38 is not providedbetween the sealing member 16 and the spacer member 56, the thickness ofthe adhesive 38 is zero. In addition, n₄ is the refractive index of thetransparent adhesive 38. d₅ is the thickness of the spacer member 54,and n₅ is the refractive index of the spacer member 54. d₆ is thethickness of the transparent adhesive 38A between the spacer members 54and 56. When the adhesive 38A is not provided between the spacer members54 and 56, the thickness of the adhesive 38A is zero. In addition, n₆ isthe refractive index of the transparent adhesive 38A. d₇ is thethickness of the spacer member 56, and n₇ is the refractive index of thespacer member 56. d₈ is the thickness of the transparent adhesive 38Bbetween the spacer member 56 and the distributed index lens 42 of theconverging lens array 40. When the adhesive 38B is not provided betweenthe spacer member 56 and the distributed index lens 42, the thickness ofthe adhesive 38B is zero. In addition, n₈ is the refractive index of thetransparent adhesive 38B.

Since the values of d₁, d₂, d₄, d₆, and d₈ are very small, the imageprinting apparatus may be actually designed so as to satisfy thefollowing expression 5:0.9×(d ₃ /n ₃ +d ₅ /n ₅ +d ₇ /n ₇)≦L _(o)≦1.1×(d ₃ /n ₃ +d ₅ /n ₅ +d ₇/n ₇)  (5).

According to this embodiment, the light-emitting panel 12 and theconverging lens array 40 are bonded to each other with the spacer unit52 interposed therebetween, which makes it possible to improve the ratioof light incident on the converging lens array 40 to light emitted fromthe light-emitting panel 12 and thus to raise the usage efficiency oflight. Therefore, it is possible to obtain the same degree of luminanceby applying, to the EL element 14, a lower voltage than that used in therelated art and thus to lengthen the life span of the EL element 14. Thebasis of an improvement in the usage efficiency of light will bedescribed later.

When the image printing apparatus is designed to satisfy the expression1, 3, or 5, it is possible to prevent defocusing between an image on thelight-emitting panel 12 and the converging lens array 40.

FIG. 7 is a cross-sectional view of the spacer members 54 and 56. Asshown in FIG. 7, light absorbing layers 66 and 68 are formed on all sidesurfaces (surfaces not facing the light-emitting panel 12 and theconverging lens array 40) of the spacer members 54 and 56. When theinternal reflection of light occurs on the side surfaces of the spacermembers 54 and 56, an image formed by the reflected light is mixed withan image formed by the light emitted from the EL element 14 to theconverging lens array 40 through the spacer members 54 and 56, whichresults in a low-definition image.

In contrast, the light absorbing layers 66 and 68 formed on the sidesurfaces of the spacer members 54 and 56 reduce the internal refectionfrom the side surfaces, which makes it possible to prevent light frombeing incident on the converging lens array 40 due to the internalreflection. Therefore, it is possible to prevent the image formed by thereflected light from being mixed with the image formed by the lightemitted from the EL element 14 to the converging lens array 40 throughthe spacer members 54 and 56.

The light absorbing layers 66 and 68 can be provided by coating a blackpigment on the side surfaces of the spacer members 54 and 56. However,in this case, there is a fear that light will be reflected from aninterface between the spacer member 54 and the light absorbing layer 66and from an interface between the spacer member 56 and the lightabsorbing layer 68 since the black pigment does not completely shieldlight. Therefore, it is preferable that the refractive indexes of thelight absorbing layers 66 and 68 be higher than those of the spacermembers 54 and 56.

When light travels from a medium having a high refractive index to amedium having a low refractive index, total reflection may occuraccording to the incident angle of light. Therefore, when the refractiveindexes of the light absorbing layers 66 and 68 are lower than those ofthe spacer members 54 and 56, the image formed by the reflected light ismixed with the image formed by the light emitted from the EL element 14to the converging lens array 40 through the spacer members 54 and 56,which results in a low-definition image. In contrast, when therefractive indexes of the light absorbing layers 66 and 68 are higherthan those of the spacer members 54 and 56, little internal reflectionoccurs from the interfaces, so that almost all light componentstraveling toward the side surfaces of the spacer members 54 and 56 areabsorbed into the light absorbing layers 66 and 68, or they pass throughthe light absorbing layers 66 and 68. Thus, the selection of a properpigment makes it possible to obtain the light absorbing layers 66 and 68having preferred refractive indexes.

Basis of Effects of this Embodiment

FIG. 8 shows an example of the path of light when a solid transmissiveelement TR1 and an air layer are arranged between the actual emissionposition and the distributed index lens 42 of the converging lens array40 (see FIGS. 3 to 5). Next, the ground of the expression 2 will bedescribed in detail.

In FIG. 8, P_(a) is a point located at the emission position wherefocusing on the distributed index lens 42 of the converging lens array40 is actually obtained. It is assumed that light is emitted from theposition P_(a) coming into contact with the transmissive element TR1. Inaddition, a indicates a distance between a position where lighttraveling from the point P_(a) on the emission position is emitted fromthe transmissive element TR1 and a line vertically drawn from the pointP_(a) on the emission position to the section of the transmissiveelement TR1. L_(o) indicates the actual object distance of theconverging lens array 40 to an object (to the light-emitting panel 12)in the air. P_(b) indicates a point separated from the converging lensarray 40 by the actual object distance thereof to the object in the air.Assuming that an air layer, not the transmissive element TR1, isprovided between the emission position and the converging lens array 40,a light beam emitted from the point P_(b) is focused on the converginglens array 40. That is, when an air layer, not the transmissive elementTR1, is provided between the emission position and the converging lensarray 40, P_(b) is a point on a virtual emission position with respectto the converging lens array 40.

In FIG. 8, the following expression 6 is established by Snell's law:n _(b)·sin θ_(b)≈sin θ_(b) =n _(a)·sin θ_(a)  (6),

where n_(b) is a refractive index of air, θ_(b) is an incident angle oflight from an interface between the air and the transmissive element TR1to the air, n_(a) is a refractive index of the transmissive element TR1,and θ_(a) is an emission angle of light from an interface between thetransmissive element TR1 and the air to the transmissive element TR1. Inthis case, since n_(a)>n_(b)≈1, the relationship θ_(b)>θ_(a) isobtained.

Further, in FIG. 8, the following expressions 7 and 8 are established:tan θ_(a) =α/d _(a)  (7), andtan θ_(b) =α/d _(b)  (8),

where d_(a) is the thickness of the transmissive element TR1, and d_(b)is a distance from the point P_(b) on the virtual emission position tothe interface between the transmissive element TR1 and the air.

The following expression 9 is obtained from the expressions 6 to 8:d _(b) =d _(a)·cos θ_(b) /n _(a)·cos θ_(a)  (9)

In a paraxial optical system using the converging lens array 40, sinceθ_(a) and θ_(b) have very small values of less than 15°, cos θ_(b)/cosθ_(a) is approximately 1. Therefore, the expression 9 can be rearrangedto the following expression 10:d _(b) =d _(a) /n _(a)  (9).

When the thickness of the air layer between the transmissive element TR1and the converging lens array 40 is d_(c), the relationshipL_(o)=d_(b)+d_(c) is established. Therefore, when the actual objectdistance L_(o) of the converging lens array 40 to an object (to thelight-emitting panel 12) in the air, the thickness d_(a) of thetransmissive element TR1, and the refractive index n_(a) satisfy thefollowing expression 11, an image formed by light passing through theactual emission position is focused on the converging lens array 40:L _(o) =d _(b) +d _(c) =d _(a) /n _(a) +d _(c)  (11).

Further, as can be seen from the above-mentioned description, thetransmissive element TR1 having a higher refractive index than that ofthe air is interposed between the emission position and the converginglens array 40, which results in an increase in the focus distance of theconverging lens array 40 to an object. That is, the point P_(a) on theactual emission position is preferably positioned further away from theconverging lens array 40 than the point P_(b) on the virtual emissionposition in order to focus an image formed by light passing through theemission position on the converging lens array 40.

FIG. 9 shows an example of the path of light when the transmissiveelement TR1 is adjacent to the entrance of light of the distributedindex lens 42 of the converging lens array 40 under the same conditionsas those in FIG. 8. In addition, FIG. 10 shows an example of the path oflight when the transmissive element TR1 is provided between thedistributed index lens 42 of the converging lens array 40 and the pointP_(a) on the actual emission position so as to be separated from themunder the same conditions as those in FIG. 8. The examples shown inFIGS. 9 and 10 differ from the example shown in FIG. 8 in the positionof the transmissive element TR1. Therefore, in this case, when theexpression 11 is satisfied, an image formed by light passing through theactual emission position is focused on the converging lens array 40.

FIG. 11A shows an example of the path of light when the solidtransmissive element TR1 and a solid transmissive element TR2 having thesame refractive index as that of the solid transmissive element TR1 areprovided between the actual emission position and the distributed indexlens 42 of the converging lens array 40. FIG. 11B shows an example ofthe path of light when the solid transmissive element TR1 and a solidtransmissive element TR2 having a different refractive index from thatof the solid transmissive element TR1 are provided between the actualemission position and the distributed index lens 42 of the converginglens array 40. In FIGS. 11A and 11B, similar to FIG. 9, the transmissiveelement TR1 is adjacent to the entrance of light of the distributedindex lens 42 of the converging lens array 40, and the transmissiveelement TR2 is interposed between the actual emission position P_(d) andthe transmissive element TR1.

In FIGS. 11A and 11B, P_(b) is a point on the virtual emission positionwhere the distributed index lens 42 of the converging lens array 40 isfocused when an air layer, not the transmissive elements TR1 and TR2, isprovided between the emission position and the converging lens array 40(which is the same as the point P_(b) shown in FIGS. 8 to 10). P_(a) isa point on the virtual emission position where the distributed indexlens 42 of the converging lens array 40 is focused when only thetransmissive element TR1 is provided between the emission position andthe converging lens array 40 (which is the same as the point P_(a) shownin FIGS. 8 to 10). In addition, P_(d) indicates a point on the emissionposition where the distributed index lens 42 of the converging lensarray 40 is actually focused. Here, it is assumed that light is emittedfrom a position P_(d) coming into contact with the transmissive elementTR2. In addition, β indicates a distance between a position where lighttraveling from the point P_(d) on the emission position is emitted fromthe transmissive element TR2 and a line vertically drawn from the pointP_(d) on the emission position to the sections of the transmissiveelements TR1 and TR2.

In FIGS. 11A and 11B, the following expression 12 is established bySnell's law:n _(b)·sin θ_(b)≈sin θ_(b) =n _(a)·sin θ_(a) =n _(d)·sin θ_(d)  (12).

In the expression 12, n_(b) is a refractive index of air; θ_(b) is anemission angle of light from an interface between the air and thetransmissive element TR1 to the air when the transmissive element TR2 isnot provided; n_(a) is a refractive index of the transmissive elementTR1; and θ_(a) is an incident angle of light from an interface betweenthe transmissive element TR1 and the air to the transmissive element TR1when the transmissive element TR2 is not provided and is an incidentangle of light from an interface between the transmissive elements TR1and TR2 to the transmissive element TR1 when the transmissive elementTR2 is provided. In this case, since n_(a)>n_(b)≈1, the relationshipθ_(b)>θ_(a) is obtained. In addition, n_(d) is a refractive index of thetransmissive element TR2; θ_(d) is an emission angle of light from theinterface between the transmissive elements TR1 and TR2 to thetransmissive element TR2 when the transmissive element TR2 is provided.In this case, since n_(d)>n_(b)≈1, the relationship θ_(b)>θ_(d) isobtained. In FIG. 11A, since the refractive index n_(a) of thetransmissive element TR1 is equal to the refractive index n_(d) of thetransmissive element TR2, the relationship θ_(d)=θ_(a) is established.

Further, in FIGS. 11A and 11B, the following expressions 13 and 14 areestablished:tan θ_(d) =β/d _(d)  (13), andtan θ_(b) =β/d _(c)  (14),

where d_(d) is the thickness of the transmissive element TR2, and d_(c)is a distance from the point P_(a) on the virtual emission position tothe interface between the transmissive elements TR1 and TR2.

The following expression 15 is obtained from the expressions 12 to 14:d _(c) =d _(d)·cos θ_(b) /n _(d)·cos θ_(d)  (15).

In a paraxial optical system using the converging lens array 40, sinceθ_(d) and θ_(b) generally have very small values of less than 15°, cosθ_(b)/cos θ_(d) is approximately 1. Therefore, the expression 15 can berearranged to the following expression 16:d _(c) =d _(d) /n _(d)  (16).

When d_(c) of the expression 16 is substituted into the expression 8obtained from FIG. 8, the following expression 17 is obtained:L _(o) =d _(b) +d _(c) =d _(a) /n _(a) +d _(c) =d _(a) /n _(a) +d _(d)/n _(d)  (17).

In FIG. 11A, since the refractive index n_(a) of the transmissiveelement TR1 is equal to the refractive index n_(d) of the transmissiveelement TR2, the following expression 18 is obtained:L _(o) =d _(a) /n _(a) +d _(d) /n _(d)=(d _(a) +d _(d))/n _(a)  (18).

Therefore, when the actual object distance L_(o) of the converging lensarray 40 to an object (to the light-emitting panel 12) in the air, thethickness d_(a) of the transmissive element TR1, the refractive indexn_(a) of the transmissive element TR1, the thickness d_(d) of thetransmissive element TR2, and the refractive index n_(d) of thetransmissive element TR2 satisfy the expression 17, an image formed bylight passing through the actual emission position is focused on theconverging lens array 40. As can be seen from the above-mentioneddescription, the transmissive elements TR1 and TR2 having a higherrefractive index than that of the air are interposed between theemission position and the converging lens array 40, which results in anincrease in the focus distance of the converging lens array 40 to anobject. That is, the point P_(d) on the actual emission position ispreferably positioned further away from the converging lens array 40than the point P_(b) on the virtual emission position in order to focusan image formed by light passing through the emission position on theconverging lens array 40.

For example, When L_(o)=2.4 mm, d_(dab =0.5) mm, and the refractiveindexes n_(a) and n_(d) of the transmissive elements TR1 and TR2 are1.52, the following is obtained: 2.4=0.5/1.52+d_(ab /1.52). Therefore,d_(a) is 3.148 mm. Thus, the distance between the actual emissionposition P_(d) and the converging lens array 40 is d_(a)+d_(ab =3.648)mm.

A general expression 2 is obtained from the above-mentioned description.In FIGS. 8 to 11B, the solid transmissive elements TR1 and TR2 are usedas an example. However, it is apparent to those skilled in the art that,when an air layer is provided between the EL elements 14 (particularly,the light-emitting layer 26) of the light-emitting panel 12 and theconverging lens array, the air layer is considered as a transmissiveelement, so that the refractive index of the air layer, which isapproximately 1, and the thickness thereof can be substituted into thegeneral expression 2. In general, an optical distance is obtained bysumming up the products of refractive indexes and thicknesses. However,in the expression 2, the optical distance is calculated by summing upthe ratios of thicknesses to refractive indexes in order to obtainfocusing on the converging lens array 40.

As described above, when a transparent spacer unit (may include atransparent adhesive) is provided between the light-emitting panel 12and the converging lens array 40, a gap between the light-emitting panel12 and the converging lens array 40 suitable for focusing an image ofthe light-emitting panel 12 on the converging lens array 40 increases,compared with the case in which only the air layer is providedtherebetween. From another viewpoint, when the gap between thelight-emitting panel 12 and the converging lens array 40 is fixed (forexample, when the light-emitting panel 12 and the converging lens array40 are fixed to the cover 13 shown in FIG. 6) and the gap is larger thanthe actual object distance of the converging lens array 40 to thelight-emitting panel 12 in the air, a spacer unit which is formed bylaminating spacer members and has a proper thickness (which includes atransparent adhesive) is provided between the light-emitting panel 12and the converging lens array 40 to increase the actual object distance.This structure enables the actual object distance to be equal the fixedgap between the light-emitting panel 12 and the converging lens array40.

Further, in this embodiment, the basis of effects of improving the ratioof light incident on the converging lens array 40 to light emitted fromthe light-emitting panel 12 and thus of raising the usage efficiency oflight will be described. In the paraxial optical system, the larger adifferent in refractive index between two media becomes, the higher therefractive index on an interface between the two media is. Therefore, asshown in FIGS. 8 and 10, when the air layer is provided between theemission position and the converging lens array 40, a considerably largeamount of light is reflected from an interface between the solidtransmissive element (for example, glass) and the air and an interfacebetween the air and the distributed index lens 42, which results in areduction in the ratio of light incident on the converging lens array 40to light emitted from the emission position. On the other hand, as shownin FIGS. 11A and 11B, when a plurality of transmissive elements isprovided between the emission position and the converging lens array 40and the refractive indexes of these transmissive elements aresubstantially equal to each other, a small amount of light is reflectedfrom interfaces between the transmissive elements (for example, glassand the adhesive 38), and a small amount of light is reflected from theinterface between the transmissive element and the distributed indexlens 42 (although the refractive index of the distributed index lens 42depends on positions, it is generally approximate to that of glass).Therefore, in this case, the ratio of light incident on the converginglens array 40 to light emitted from the emission position is high.

In the above-mentioned embodiment, the spacer member is provided betweenthe light-emitting panel 12 and the converging lens array 40. When thelight-emitting panel 12 is adhered to the converging lens array 40 orwhen the spacer member is adhered to the light-emitting panel 12 or theconverging lens array 40, an adhesive having a refractive index close tothat of glass is used. Therefore, it is possible to more improve theusage efficiency of light, compared to the related art shown in FIG. 1.

FIG. 12A shows outmost light components which are emitted from one spotto the photosensitive drum 110 via the distributed index lens 42 whenonly an air layer is provided between the sealing member 16 of thelight-emitting panel 12 and the converging lens array 40. FIG. 12B showsoutmost light components which are emitted from one spot to thephotosensitive drum 110 via the distributed index lens 42 when thespacer member 50 is provided between the sealing member 16 of thelight-emitting panel 12 and the converging lens array 40. In FIG. 12A,the traveling angle of the outmost light component in the air layer isθ_(b). When the sealing member 16 is formed of glass, that is, has arefractive index n_(a) of 1.52, and the traveling angle of light in thesealing member 16 is 8°, θ_(b)=12.30 is obtained by Snell's law. On theother hand, in FIG. 12B, the traveling angle of the outmost lightcomponent in the spacer member 50 is θ₅₀. When the sealing member 16 andthe spacer member 50 are formed of glass, that is, have a refractiveindex n_(a) of 1.52, and the traveling angle of light in the sealingmember 16 is 8°, θ₅₀=8° is obtained by Snell's law.

As shown in FIG. 12A, when only the air layer is provided between thesealing member 16 of the light-emitting panel 12 and the converging lensarray 40, a distance between the sealing member 16 and the distributedindex lens 42 becomes small, and thus the allowance of the distancebecomes small. For example, when the distance is larger than apredetermined value, the traveling angle θ_(b) of light in the air layerbecomes large. As a result, a large amount of light travels outside thedistributed index lens 42 without traveling toward the distributed indexlens 42, resulting in low usage efficiency of light. On the other hand,when the distance is smaller than a predetermined value, a diameterd_(s) of a spot focused on the photosensitive drum 110 becomes large. Asa result, the resolution of a latent image formed on the photosensitivedrum 110 is lowered.

In contrast, as shown in FIG. 12B, when the spacer member 50 is providedbetween the sealing member 16 of the light-emitting panel 12 and theconverging lens array 40, a distance between the sealing member 16 andthe distributed index lens 42 increases, which results in an increase inthe allowance of the distance. Therefore, it is possible to reducedefects, compared with the example shown in FIG. 12A.

Manufacturing Method of Electro-Optical Device

Next, a manufacturing method of the above-mentioned electro-opticaldevice will be described. First, the converging lens array 40 and thelight-emitting panel 12 are prepared, and the object distance L_(o) ofthe converging lens array 40 to the light-emitting panel 12 in the airis measured. Then, the thickness of a spacer unit to be used iscalculated so as to satisfy the expression 1, preferably, the expression2, on the basis of the object distance L_(o) and the refractive indexand the thickness of the spacer member to be used (on the basis of therefractive index and thickness of an adhesive at the time of hardeningwhen the refractive index and thickness of the adhesive are considered).Subsequently, a combination of spacer members constituting the spacerunit is determined on the basis of the calculated thickness of thespacer unit. More specifically, a plurality of spacer members havingdifferent thicknesses is prepared in advance, and the spacer members areselected so that the thickness of a combination of spacer members issubstantially equal to the calculated thickness of the spacer unit. Forexample, as shown in FIG. 13, spacer members 54, 56, and 58 are selectedas members constituting the spacer unit 52.

Next, as shown in FIG. 14, the plurality of spacer members 54, 56, and58 are laminated and bonded to each other by an adhesive, therebyobtaining the spacer unit 52. Then, as shown in FIG. 15, the converginglens array 40 is bonded to the spacer member 58, which is an outmostlayer of the spacer unit 52, by, for example, an adhesive, and thelight-emitting panel 12 is bonded to the spacer member 54, which is theother outmost layer of the spacer unit 52, by, for example, an adhesive.In this way, as shown in FIGS. 16 and 17, an electro-optical devicehaving the light-emitting panel 12 and the converging lens array 40bonded to each other with the spacer unit 52 interposed therebetween isobtained. However, a process for bonding the spacer members 54, 56, and58, a process for bonding the spacer member 54 to the light-emittingpanel 12, and a process for bonding the spacer member 58 to theconverging lens array 40 may be performed randomly or at the same time.When the expression 1, preferably, the expression 2 is satisfied, thespacer unit 52 having a thickness suitable for the actual objectdistance of the converging lens array 40 is obtained, so that an imageon the light-emitting panel 12 is substantially focused on theconverging lens array 40.

As shown in FIGS. 18 to 20, it is preferable that the adhesive 38B bearranged on the spacer member 58 of the spacer unit 52 adjacent to theconverging lens array 40 and a receiving hole 70 to which the converginglens array 40 is fitted be formed in the spacer member 58. In this way,since the adhesive 38B is hardened in the receiving hole 70, theadhesive 38B can be cleanly formed therein. In addition, the receivinghole 70 enables the converging lens array 40 to be accurately arrangedon the spacer unit 52. In particular, as shown in FIGS. 19 and 20, thereceiving hole 70 has an inner side surface parallel to a lengthwiseside surface of the converging lens array 40, and it is preferable thatthe length of the inner surfaces be substantially equal to the width ofthe converging lens array 40. Since the adhesive 38B is filled into thereceiving hole 70 so as to closely adhere to the inner surface thereof,the hardened adhesive 38B has a flat side surface parallel to thelengthwise side surface of the converging lens array 40. Alternatively,widthwise side surfaces of the converging lens array 40 may be separatedfrom the side surface of the receiving hole 70. Therefore, the adhesive38B may protrude from the widthwise side surfaces of the converging lensarray 40 and the light-emitting panel 12, or it may be recessed a littlefrom the widthwise side surfaces thereof. In order to obtain focusing onthe converging lens array 40 as expected, the adhesive 38B should becompletely arrange in an optical path from the EL element 14 of thelight-emitting panel 12 to the distributed index lens 42 of theconverging lens array 40. In order to achieve this object, the adhesive38B can be easily applied by making the adhesive before hardened flow inthe lengthwise direction of the converging lens array 40 and thelight-emitting panel 12 while bringing the adhesive 38B into contactwith the lengthwise side surface of the receiving hole 70. As a result,the hardened adhesive 38B has a flat side surface parallel to thelengthwise side surfaces of the converging lens array 40 and thelight-emitting panel 12, but is not flush with the widthwise sidesurfaces thereof.

As shown in FIGS. 21 and 22, it is preferable that the side surface ofthe receiving hole 70 of the spacer member be provided with concaveportions 72 or 73 into which the transparent adhesive 38B for adheringthe converging lens array 40 to the spacer member 58 is filled from thebottom surface of the receiving hole 70. It is difficult to arrange theadhesive 38B before hardened in only necessary portions of the receivinghole 70 since the adhesive 38B has fluidity. However, the residualadhesive 38B is filled into the concave portions 72 or 73 formed in theside surface of the receiving hole 70. In this way, the adhesive 38B canmore reliably contact the side surface of the receiving hole 70, and itis possible to reduce the amount of the adhesive 38 flowing outside thereceiving hole 70 to the minimum and thus to improve the appearance ofan electro-optical device.

Further, as shown in FIGS. 23 and 24, it is preferable that, in additionto the receiving hole 70 of the spacer member 58 (or instead of thereceiving hole 70), the adhesive 38 be arranged on the spacer member 54of the spacer unit 52 adjacent to the light-emitting panel 12 and that areceiving hole 71 for fitting the light-emitting panel 12 be formed inthe spacer member 54. Since the adhesive 38 is hardened in the receivinghole 71, the adhesive 38 can be cleanly formed therein. In addition, thereceiving hole 71 enables the light-emitting panel 12 to be accuratelyarranged on the spacer unit 52. As shown in FIG. 24, the receiving hole70 has an inner side surface parallel to a lengthwise side surface ofthe sealing member 16 of the light-emitting panel 12, and it ispreferable that the length of the inner surface be substantially equalto the width of the sealing member 16. In this way, the adhesive 38 canbe easily applied by making the adhesive 38 before hardened flow in thelengthwise direction of the converging lens array 40 and thelight-emitting panel 12 while bringing the adhesive 38B into contactwith the lengthwise side surface of the receiving hole 71. As a result,the adhesive 38 can be completely arrange in an optical path from the ELelement 14 of the light-emitting panel 12 to the distributed index lens42 of the converging lens array 40. The concave portions 72 or 73 may beprovided in the receiving hole 71.

Further, as shown in FIGS. 25 and 26, the spacer unit 52 may be providedwith receiving holes 75 and 76 in which the transparent adhesives 38 and38B for adhering the light-emitting panel 12 and the converging lensarray 40 to the spacer unit 52 are respectively arranged. In this way,since the adhesives 38 and 38B are hardened in the receiving holes 75and 76, respectively, the adhesives 38 and 38B can be cleanly formedtherein. The concave portions 72 or 73 may be provided in the receivingholes 75 and 76. The receiving hole 75 or the receiving hole 76 may notbe provided, and the receiving holes 71 and 75 may be formed in thespacer unit. In addition, the receiving holes 70 and 76 may be formed inthe spacer unit.

Furthermore, as shown in FIG. 27 or 28, grooves 78 and 79 into which theadhesives 38 and 38B flow may be formed in both surfaces of the spacerunit 52, respectively. A pair of grooves 78 extending in the lengthwisedirection of the space unit 52 are formed in the surface of the spacermember 58 of the spacer unit 52, and a pair of grooves 79 extending inthe lengthwise direction of the space unit 52 are formed in the surfaceof the spacer member 54 of the spacer unit 52. As shown in FIGS. 29 and31, the adhesive 38 is arranged between the pair of grooves 78. As shownin FIG. 31, the adhesive 38B is arranged between the pair of grooves 79on the other side. As shown in FIGS. 30 and 31, the converging lensarray 40 is arranged at the center of the surface of the space member58, with the edge thereof overlapping the grooves 78, and is thenadhered thereto. As shown in FIG. 31, the sealing member 16 is arrangedat the center of the surface of the space member 54, with the edgethereof overlapping the grooves 79, and is then adhered thereto.

It is difficult to arrange the adhesives 38 and 38B before hardened inonly necessary portions of the spacer unit 52 since the adhesives 38 and38B have fluidity. However, as shown in FIG. 31, the residual adhesives38 and 38B are filled into the grooves 78 and 79 formed in the spacerunit 52. In this way, it is possible to reduce the amount of theadhesives 38 and 38B flowing from a gap between the spacer unit 52 andthe light-emitting panel 12 or the converging lens array 40 to theoutside to the minimum and thus to improve the appearance of anelectro-optical device. The grooves may be provided in only one surfaceof the spacer unit 52.

Image Printing Apparatus

As described above, the electro-optical device (for example, theelectro-optical device 10B) according to this embodiment can be used asa linear optical head for writing a latent image on an image carrier ofan image printing apparatus using an electrophotography method. Theimage printing apparatus includes, for example, a printer, a printingpart of a copy machine, and a printing part of a facsimile.

FIG. 32 is a longitudinal cross-sectional view illustrating an exampleof an image printing apparatus using any one of the electro-opticaldevices according to this embodiment as a linear optical head. Thisimage printing apparatus is a tandem full color image printing apparatususing a belt intermediate transfer method.

In this image printing apparatus, four organic EL array exposure heads10K, 10C, 10M, and 10Y having the same structure are arranged atexposure positions of four photosensitive drums (image carriers) 110K,110C, 110M, and 110Y having the same structure. The organic EL arrayexposure heads 10K, 10C, 10M, and 10Y correspond to any one of theelectro-optical devices according to this embodiment.

As shown in FIG. 32, the image printing apparatus has a driving roller121, a driven roller 122, an endless intermediate transfer belt 120wound around the driving roller 121 and the driven roller 122, and theintermediate transfer belt 122 circulates around the rollers 121 and 122in the direction of arrow shown in FIG. 32. Although not shown, atension applying unit for applying tension to the intermediate transferbelt 120, such as a tension roller, may be provided.

The four photosensitive drums 110K, 110C, 110M, and 110Y are disposed atpredetermined intervals around the intermediate transfer belt 120. Eachphotosensitive drum has a photosensitive layer on the outer peripheralsurface thereof. Suffixes ‘K’, ‘C’, ‘M’, and ‘Y’ added to referencenumerals indicate black, cyan, magenta, and yellow, respectively. Thisis similarly applied to other members. The photosensitive drums 110K,110C, 110M, and 110Y are rotated in synchronism with the driving of theintermediate transfer belt 120.

A corona charger 111 (K, C, M, and Y), an organic EL array exposure head10 (K, C, M, and Y), and a developing device 114 (K, C, M, and Y) arearranged around each photosensitive drum 110 (K, C, M, and Y). Thecorona charger 111 (K, C, M, and Y) uniformly charges the outerperipheral surface of the corresponding photosensitive drum 110 (K, C,M, and Y). The organic EL array exposure head 10 (K, C, M, and Y) writesan electrostatic latent image on the charged outer peripheral surface ofthe photosensitive drum. Each organic EL array exposure head 10 (K, C,M, and Y) is arranged in such a manner that a plurality of OLED elements14 is arranged along a bus (in the main scanning direction) of thephotosensitive drum 110 (K, C, M, and Y). The writing of theelectrostatic latent image is performed by radiating light emitted fromthe plurality of OLED elements 14 on the photosensitive drum. Thedeveloping device 114 (K, C, M, and Y) applies toner as a developer ontothe electrostatic latent image to form a toner image, that is, a visibleimage on the photosensitive drum.

Black, cyan, magenta, and yellow toner images formed by single-colortoner image forming stations for the four colors are sequentiallyprimarily transferred onto the intermediate transfer belt 120 so as tobe superimposed on the intermediate transfer belt 120, thereby forming afull-color toner image. Four primary transfer corotrons (transferdevices) 112 (K, C, M, and Y) are arranged inside the intermediatetransfer belt 120. The primary transfer corotrons 112 (K, C, M, and Y)are arranged in the vicinities of the photosensitive drums 110 (K, C, M,and Y), respectively, and electrostatically attract the toner imagesfrom the photosensitive drums 110 (K, C, M, and Y) to transfer the tonerimages onto the intermediate transfer belt 120 passing between thephotosensitive drums and the primary transfer corotrons.

Finally, sheets 102, which are image forming targets, are fed one by onefrom a paper feed cassette 101 to a nip between a secondary transferroller 126 and the intermediate transfer belt 120 coming into contactwith the driving roller 121 by a pick-up roller 103. The full-colortoner image on the intermediate transfer belt 120 are collectivelysecondary-transferred onto one surface of the sheet 120 by the secondarytransfer roller 126 and is then fixed on the sheet 120 by a pair offixing rollers 127 serving as a fixing unit. Then, the sheet 102 isdischarged onto a paper discharge cassette formed on the upper side ofthe apparatus by a pair of paper discharge rollers 128.

The image printing apparatus shown in FIG. 32 uses any one of theelectro-optical devices using an organic EL array as a writing unit,which makes it possible to improve the usage efficiency of light.

Next, another embodiment of the image printing apparatus according tothe invention will be described.

FIG. 33 is a longitudinal cross-sectional view illustrating anotherimage printing apparatus using any one of the electro-optical devicesaccording to this embodiment as a linear optical head. This imageprinting apparatus is a rotary-development-type color image printingapparatus using a belt intermediate transfer method. In the imageprinting apparatus shown in FIG. 33, a corona charger 168, a rotarydeveloping unit 161, an organic EL array exposure head 167, and anintermediate transfer belt 169 are provided around a photosensitive drum(an image carrier) 165.

The corona charger 168 uniformly charges the outer peripheral surface ofthe photosensitive drum 165. The organic EL array exposure head 167writes an electrostatic latent image on the charged outer peripheralsurface of the photosensitive drum 165. The organic EL array exposurehead 167 is any one of the electro-optical devices according to theabove-mentioned embodiment and is arranged in such a manner that aplurality of OLED elements 14 is arranged along a bus (in the mainscanning direction) of the photosensitive drum 165. The writing of theelectrostatic latent image is performed by radiating light emitted fromthe plurality of OLED elements 14 on the photosensitive drum.

The developing unit 161 is a drum including four developing devices163Y, 163C, 163M, and 163K arranged at right angles to each other, andcan be rotated on a shaft 161 a in the counterclockwise direction. Thedeveloping devices 163Y, 163C, 163M, and 163K supply yellow, cyan,magenta, and black toners to the photosensitive drum 165 to attach thetoners as a developer onto the electrostatic latent image, therebyforming a toner image, that is, a visible image on the photosensitivedrum 165.

The endless intermediate transfer belt 169 is wound around a drivingroller 170 a, a driven roller 170 b, a primary transfer roller 166, anda tension roller, and circulates around these rollers in the directionof arrow shown in FIG. 33. The primary transfer roller 166electrostatically attracts the toner image from the photosensitive drum165 to transfer the toner image onto the intermediate transfer belt 169passing between the photosensitive drum and the primary transfer roller166.

More specifically, at the first rotation of the photosensitive drum 165,an electrostatic latent image for a yellow (Y) image is written by theexposure head 167, and a toner image having the same color is formed bythe developing device 163Y and is then transferred onto the intermediatetransfer belt 169. At the next rotation thereof, an electrostatic latentimage for a cyan (C) image is written by the exposure head 167, and atoner image having the same color is formed by the developing device163C and is then transferred onto the intermediate transfer belt 169 soas to overlap the yellow toner image. When the photosensitive drum 169makes four rotations in this way, yellow, cyan, magenta, and black tonerimages sequentially overlap each other on the intermediate transfer belt469, so that a full-color toner image is transferred onto theintermediate transfer belt 169. Finally, when images are formed on bothsurfaces of a sheet, which is an image forming target, a toner imagehaving a color common to the front and rear surfaces is transferred ontothe intermediate transfer belt 169, and then a toner image having thenext color common to the front and rear surfaces, thereby transferring afull-color toner image on the intermediate transfer belt 169.

A sheet transfer path 174 through which a sheet passes is provided inthe image printing apparatus. The sheets are fed one by one from thepaper feed cassette 178 by the pick-up roller 179 and are thentransferred along the sheet transfer path 174 by a transfer roller.Then, the sheets pass through a nip between a secondary transfer rollerand the intermediate transfer belt 169 coming into contact with thedriving roller 170 a. The secondary transfer roller 171 collectively andelectrostatically attracts the full-color toner image from theintermediate transfer belt 169 to transfer the toner image onto onesurface of the sheet. The secondary transfer roller 171 approaches or isseparated from the intermediate transfer belt 169 by a clutch (notshown). When a full-color toner image is transferred onto a sheet, thesecondary transfer roller 171 abuts on the intermediate transfer belt169. On the other hand, when the toner images overlap the intermediatetransfer belt 169, the secondary transfer roller 171 is separatedtherefrom.

In this way, the sheet having an image thereon is transferred to afixing device 172 and passes between a heating roller 172 a and apressing roller 172 b of the fixing device 172, thereby fixing a tonerimage on the sheet. The sheet having the fixed toner image istransferred to the pair of paper discharge rollers 176 to be carried inthe direction of arrow F. When printing is performed on both sides of asheet, after most of the sheet passes through the paper dischargerollers 176, the pair of paper discharge rollers 176 is reverselyrotated to transfer the sheet in a double-sided printing transfer path175 as represented by an arrow G. Subsequently, a toner image istransferred onto the other surface of the sheet by the secondarytransfer roller 171, and is then fixed by the fixing device 172. Then,the sheet is discharged to the outside by the pair of paper dischargerollers 176.

The image printing apparatus shown in FIG. 33 uses the exposure head 167(any one of the electro-optical devices according to the above-mentionedembodiment) having an organic EL array as a writing unit, which makes itpossible to improve the usage efficiency of light.

The image printing apparatus capable of using any one of theelectro-optical devices according to the above-mentioned embodiment hasbeen described as an example. However, any one of the electro-opticaldevices according to the above-mentioned embodiment can be applied toimage printing apparatuses adopting other electrophotography methods,and these image printing apparatuses can be also included in the scopeof the invention. For example, the electro-optical devices according toinvention can be applied to an image printing apparatus which directlytransfers a toner image on a photosensitive drum without using theintermediate transfer belt and an image printing apparatus capable offorming monochrome images.

Applications

The electro-optical device according to the invention can be applied tovarious exposure devices and illuminating devices.

In the light-emitting panel of the above-mentioned electro-opticaldevice, OLED elements are used as light-emitting element for convertingelectrical energy into optical energy. However, other light-emittingelements (for example, inorganic EL elements or plasma display elements)may be used for the light-emitting panel. In addition, abottom-emission-type light-emitting panel may be used. In thebottom-emission-type light-emitting panel, light is emitted from thelight-emitting elements to the outside through a transparent substrate.The spacer unit may be arranged between the substrate and the converginglens array.

Further, in the above-mentioned electro-optical device, the converginglens array 40 is attached to the light-emitting panel havinglight-emitting element therein. However, the converging lens array maybe attached to a light value panel having a plurality of light valuepixels therein. The light value pixels change the transmittance of lightby electrical energy supplied, and include pixels of a liquid crystaldisplay device, pixels of an electro-luminescent display device, pixelsof an electrophoresis display device, and pixels of adispersed-particle-alignment-type display device. These pixels adjustthe transmission amount of light emitted from an individual lightsource. Instead of the light-emitting panel 12, for example, a lightvalue panel, such as a light crystal panel, may be attached to a microlens array so that light emitted from an individual light source passesthrough the light value panel and the converging lens array. Thiselectro-optical device can be used for a projector for projecting imagesonto a screen, in addition to the image printing apparatuses shown inFIGS. 32 and 33.

1. An electro-optical device comprising: an electro-optical panel whichhas a plurality of electro-optical elements whose light-emittingcharacteristics or transmissive characteristics are changed byelectrical energy applied; a converging lens array which has a pluralityof distributed index lenses, each transmitting light traveling from theelectro-optical panel to form an erect image with respect to an image onthe electro-optical panel, the images formed by the plurality ofdistributed index lenses constituting a continuous image; and atransmissive spacer unit which is provided between the electro-opticalpanel and the converging lens array so as to be bonded to them, whereinthe spacer unit includes a laminated structure of a plurality oftransmissive spacer members.
 2. The electro-optical device according toclaim 1, wherein the spacer unit has light absorbing layers formed onsurfaces thereof not facing the electro-optical panel and the converginglens array.
 3. The electro-optical device according to claim 1, whereinthe spacer unit is provided with a receiving hole into which atransparent adhesive for adhering at least one of the electro-opticalpanel and the converging lens array to the spacer member is filled. 4.The electro-optical device according to claim 3, wherein at least one ofthe electro-optical panel and the converging lens array is fitted intothe receiving hole.
 5. The electro-optical device according to claim 3,wherein concave portions into which the adhesive flows from the bottomof the receiving hole are formed in a side surface of the receiving holeof the spacer unit.
 6. The electro-optical device according to claim 1,wherein grooves into which a transparent adhesive for adhering at leastone of the electro-optical panel and the converging lens array to thespacer unit flows are formed in a surface of the spacer unit facing atleast one of the electro-optical panel and the converging lens array. 7.The electro-optical device according to claim 1, wherein, when therefractive index of each transmissive element provided betweenelectro-optical elements of the electro-optical panel and the converginglens array is n_(i), the thickness of each transmissive element isd_(i), the number of transmissive elements is m, and an object distanceof the converging lens array to the electro-optical panel in the air isLo, the following expression 1 is satisfied: $\begin{matrix}\lbrack {{Expression}\quad 1} \rbrack & \quad \\{{0.9 \times {\sum\limits_{i = 1}^{m}\frac{d_{i}}{n_{i}}}} \leq L_{o} \leq {1.1 \times {\sum\limits_{i = 1}^{m}\frac{d_{i}}{n_{i}}}}} & (1)\end{matrix}$
 8. An image printing apparatus comprising: image carriers;charging devices that charge the image carriers; the electro-opticaldevice according to claim 1 that radiates light emitted from theelectro-optical panel to the converging lens array onto charged surfacesof the image carriers to form latent images thereon; developing devicesthat attach a toner on the latent images to form toner images on theimage carriers; and a transfer device that transfers the toner imagesfrom the image carriers to another object.
 9. A method of manufacturingthe electro-optical device according to claim 1, comprising: laminatinga plurality of spacer members such that the spacer members are bonded toeach other; bonding any one of the spacer members to the electro-opticalpanel; and bonding another member of the spacer members to theconverging lens array.
 10. The method of manufacturing anelectro-optical device according to claim 9, further comprising:measuring an actual object distance L_(o) of the converging lens arrayto the electro-optical panel in the air; and calculating the thicknessof the spacer unit to be used, on the basis of the object distance L_(o)and the refractive indexes of the spacer members, so as to satisfy theexpression 1.